Consturction of street pavements



Patented July 17, 1928.

UNITED STATES PATENT OFFICE.

BROTHERS COMPANY, OF CAMBRIDGE, MASSACHUSETTS, A CORPO RATION OF WEST VIRGINIA.

No Drawing.

This invention relates particularly to such pavements and surface structures asare composed of two layers placed upon a foundation in which the lower layer 1s relatively thick, inch and one'half to two inches or more, and the upper layer relatively th1n and approximately one-half to three quarters of an inch or even thinner.

In the laying of such pavements, greatcare is exercised in order to make the upper and wearing layer firmly adhere and become part of the lower supporting layer. For if a complete and perfect juncture is not caused between those layers, the upper layer w1ll peel off and will be broken .up. To secure to the lower bituminous layer which is usually composed of particles of stone, having its voids filled with smaller stone and sand, cemented with bitumen, the thinner upper layer, composed of mineral aggregate of any desired kind, also cemented with bitumen, it is now customary to lay the lower layer upon a foundation, spread it in a thick layer, and, before rolling, spread the second layer immediately upon itand roll the two layers simultaneously. Another method is to lay the lower layer and roll it only slightly and, while still hot and still plastic, apply the upper and thin layer and roll them'together. Both these methods are faulty in construction in that they prevent the lower layer from getting the necessary compression for good construction. The upper layer cushions the lower layer and preventsthe easy movements of the particles as well as distributes the pressure of the roller, so that the lower particles are not compressed. A further disadvantage of. the above mentioned constructions is the resultant wavy surface which is the result of the simultaneous rolling of the two courses. The roller in travelling over the hot laid surface pushes and shoves the thin layer into irregular ridges and causes multitudinous hair cracks which are always seen in such construction. A

still further disadvantage is the physical impossibility of spreading and laying the upper thin surface upon the lower course uniformly. In raking the lower surface, depressions are made with the rake, with the shovels and even with the feet of the rakers themselves, which depressions are filled with the material used for the upper coating, and causing it to be in some places an inch or an CONSTRUCTION 03 STREET PAVEMENTS.

Application filed September 10, 1925. Serial No. 55,619.

face, full of check marks and hair lines.

My invention obviates all these defects and contemplates the lower course of bitumen-coated mineral aggregate laid either hot or cold, rolled with a heavy roller until solid and compact, and until the surface is practically cold and has received its maximum compression. After this layer is cold, rigid and inflexible, before laying the thin upper coat, I subject the superficial surface of the lower course to heat applied in any suitable form, so as to warm, heat and liquefy the bitumen composing the upper quarter of an inch or so of the lower course, and while this superficial layer is hot, I immediately place upon it the thin wearing surface and roll it into unison with the bottom layer. Thus, I have a rigid, solid, well rolled foundation which is even in contour. and upon which the surfacing can be spread evenly and uniformly, andwhich, on account of thethin preheated layer, will stick and mute perfectly with the lower course. Such mixture will not crepe or Wave under the roller either during the process of rollmg or subsequently, for the foundation itself is not plastic and yielding, but hard. solid and rigid, causing the whole pressure of the roller when compressing the upper layer to beborne by the upper layer itself,

,which causesvit not only to unite withthe heated superficialsurface of the lower layer. but also to enter any and all superficial voids which maybe contained in thelower laver. due to its coarse composition. U I

Anoth r advantage of my construction is that a great economy could be achieved in the upper layerwhich is usually the most expensive layer, containing better selected aggregate as Well as a greater amount of bitumen, which is the most'ex iiensive ingredient. The reason for this is obvious, for it is easier to spread and lay a thin layer upon a Smooth, hard surface, than to attempt to lay the same layer upon a surface full of irregularities and yielding to the slightest pressure. A half inch layer,

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laid on top of the lower surface, according to my invention, will vary very little from one-halt inch, while, it laid by the old processes, may be from one quarter inch to one inch thickness.

To practise my invention, I lay preferably one inch and a half or thereabouts of a mixture composed of mineral aggregates and bitumen. "he exact composition of this layer of no particular importance, and may be one of the well known types such as is well known in the paving art, as binder, close binder, asphaltie concrete, bitulithic or cold laid mixtures, laid either with a colloidal as ahalt or with a temaorar li uetied l 1 l 3 q 'compound.

The sole requisite of this lower layer is that it must be otsuch nature that, after being thoroughly rolled and cold, it should form a rigid load-carrying layer, one that is thick enough and rigid enough to sustain the loads to which the road is subjected; on roads exposed to heavy tratlic, this layer is thicker and better than on residential streets. Alter this layer has been thoroughly rolled, and has become cold or at least cold enough to resist the undulatory motions of the roller, I heat, by means of a suitable burner, 01' heater, the upper one quarter of an inch or so of this load-carrying layer, and immediately, while the bitumen of the superficial surface of this layer is still hot, I. lay upon it and roll into it, the surface layer which is composed of mineral aggregate and bitumen having preferably a larger amount of bitumen than the lower layer. This upper thin layer may be of any desired mineral aggregate and necessarily must be composed of line aggregate on account of its thickness. it may be composed of finely crushed stone with or without the stone dust, of crushed stone and sand. or of mixtures of clay, with various mineral aggregates, and bitumen or may be composed of the above materials or any of theminixed with bitumen. It also may be composed of ordinary coarse sand to which a hardened or toughened bitumen has been added. The whole object to produce a tough, wear resisting, upper layer wni ch is relatively rich in bitumen, and which is securely fastened to the lower course, and which is of uniform thickness tl'irmighout, and does not check in nov ce-o rolling thus producing a scientifically uniform and correct pavement instead oi the haphazard results which necessarily are the outcomeoit the present methods. The upper layer being thin and uniform, can be mad, rich in bitumen, for, being uniform in thickness, it will not roll and will not form into waves and pockets. if the lower layer should, on account o'l rain or or causes, become dirty, it can be treated with small amount of: bitumen which is sprinkled upon its surface before the application of the heat, thus rendering the surface receptive and retentive of the subsequently laid upper layer.

T he burner or heater with which I prefer to heat the superficial layer of the lower course is an oil burner wnich can easily be moved over the surface, or an be any easily propelled device heated by oil, or steam pro-. ducing direct or indirect heat.

l i hat- I claim as my invention is I. A method of constructing a roadway by laying upon a suitable foundation, a relatively thick layer of a mixture composed ot a mineralaggregate and bitumen, cai iable of supporting the load to which it'is subjected, rolling, tam iing and consolidating this layer until cold and solid and incapable of being further distorted; then melting by heat the superlicial layer of this lower layer and then placing upon it a wear resisting thin layer, and again rolling it into unison andclose contact with the bottom layer, thus producing a roadway having a lower course relatively thick and heavily connpactcd, an upper course relatively thin, bound and cemented together into one inseparable layer.

2. A method of constructing aroadway by securely lastel'iing and. binding a wear resisting layer to a load carrying layer. by melting by heat a thin superficial section of the load carrying layer before applying the wear resisting layer and rolling both into intimate and close contact.

3. A roadway composed of a solidly packed load carrying layer and a relatively rich thin weara'esisting layer-superimposed thereon and bonded thereto when the upper surface of said compressed load carrying layer and said thin wear resisting layer are in a heated state.

AUGUST E. SCHUTTE. 

